This report is spun off from bug#69385 at the request of Eli Zaretskii, because it concerns a problem that seems to be independent of that bug report, though like it involves long lines of bidirectional text. When I visited a certain elisp file generated by a program of mine and type `M-v', it took some time (see below for details) for the display to scroll to 4% from the top (according to the mode line) and then there was no further change and Emacs froze, using 100% of a CPU core. I found no way to unfreeze it within Emacs and after about 15 minutes terminated the emacs process from the shell. This is reliably reproducible with this file. The file in question is only about 50k bytes long, but it contains one line of more than 37k characters, consisting of a mix of ASCII and non-ASCII characters, including properly shaped Arabic script. The file itself has base paragraph direction LTR. Most of the Arabic words in this file are enclosed in the bidirectional control characters POP DIRECTIONAL FORMATTING (#x202c) and RIGHT-TO-LEFT EMBEDDING (#x202b). I did not add these characters, but I had copy-&-pasted most of the Arabic from a PDF file I did not create. I don't know if PDFs of Arabic text normally contain these control characters, but the consequences for Emacs were dramatic. When I simply visited this file in Emacs (started with -Q) there was an immediate slowdown, and in top I could see Emacs using 100% of a CPU thread. I ran `M-: (benchmark-run nil (end-of-buffer))' on this file, and the result was: (27.962602113 2 0.0226042269999999977) This timing is from a build from master including the patch Eli posted in bug#69385 (see https://lists.gnu.org/archive/html/bug-gnu-emacs/2024-03/msg00101.html). On a build without that patch, the benchmark timing is very much longer. The display of the benchmark result only appeared in the echo area after more than a minute (I timed it with a stopwatch). At that point the mode line showed the buffer at 4% from the top, and the display remained frozen afterwards. After several minutes during which Emacs consumed 100% CPU, and I had switched the focus away from the Emacs frame, the CPU consumption stopped, but as soon as I switch focus back to that frame, it went back to 100%. The display never changed from showing the buffer at 4%, apparently being in some kind of infinite loop. After about 15 minutes I started gdb, attached the Emacs process and produced a backtrace, which I've attached, in the hope it helps to diagnose the problem. The problem seems to be certainly related the the bidirectional control characters, because I made a copy of the file and removed all occurrences of these control characters from it, and then ran the end-of-buffer benchmark, getting this result (with Eli's patch): (0.716104165 4 0.04223660400000001) And the display updated normally and CPU consumption was normal. Nevertheless, there seems to be something else besides the control characters involved in this issue, because as a further test, I created a buffer consisting of more than 1000 copies of the test string concatenating the Arabic example in etc/HELLO and "Hello" (see bug#69385 for more on such test buffers), and manually enclosed each Arabic word in the above control characters, but the benchmark result in this buffer was not significantly different from the result without the control characters (and similar to the above result for the copy of the problematic file without the control characters), and the display did not freeze. (I have emailed a copy of the problematic file to Eli, at his request. I do not want to post it publicly, because it contains hundreds of text snippets from a PDF of a copyrighted book. Each snippet is certainly within the bounds of fair use for distribution, but in the sum probably not.) In GNU Emacs 30.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.38, cairo version 1.18.0) of 2024-03-04 built on strobelfs2 Repository revision: b3eb49a4661e31306555e82bdf24db6c36d67ad2 Repository branch: master Windowing system distributor 'The X.Org Foundation', version 11.0.12101009 System Description: Linux From Scratch r12.0-112 Configured using: 'configure -C --with-xwidgets 'CFLAGS=-Og -g3' PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig' Configured features: ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM XWIDGETS GTK3 ZLIB Important settings: value of $LANG: en_US.UTF-8 locale-coding-system: utf-8-unix
txtKKxnYu62oB.txt
Description: gdb backtrace
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